Single-line hydraulic system



Sept. 27, 1949.

Filed May 27, 1944 N. D. OWEN SINGLE-LINE HYDRAULIC SYSTEM 2 Sheets-Sheet 1 /Vnsse-P '0. OWEN A TTORNEYJ' N. D. OWEN SINGLE-LINE HYDRAULIC SYSTEM 2 Sheets-Sheet 2 Sept. 27, 1949.

Filed May 27, 1944 Patented Sept. 27, 1949 fici-antec lander insect amended April:` 30,"v 19 elinventiori described herein maylben'ia'nu-y facturedaandfused by or for theGovernmenitfor governmental purposesyfwithoutithe payment tome'orally/:royalty;thereon;V vv,i I -.-.\T his ,invention relates to hydrauliclsystems'and more-.particularly .to apparatus for controlling a hydraulic servomotor atv a fp'ointl remote -from the* operatorthroughasinglefpipe.- Anjobjectp theinventionfs` to zgenerally "-s'im-'l -Dlify devices.ofthischaracters. wiwi 10 ...More speciiically, ianobj ect .of the iinvention iis '.eliminate.y aconsiderable portion of Athe piping: usuallgfrequiredin .systems .of thisfkindi 1 f. f f otherobject .ispo simplify :lzheiva'lvingv in a device'of thisggeneral character.A f: IO merlolbjectsand i. advantages -;Wil1-.;appear.ias;1 eference';

the 'invention :isQ furtherv ,described -andfr Fig. 1 .schematic view of Aanv embodiment of miivnuoinitssimplestfprm e.. "another schematioviewfof the invengfa 'modiiicationof certain par-tss 'anotherv schematic ,viewy g showing. air 1 ofthe.pumpinsmeansoftne system. "Si" "ila referenc..charactersrefer.; to similar tlrbiiitthelseveral gurespfzthe draws is4 ifad to' the drawing. wherei SYSTEM misser D; wngmbuqiierque, N. Mex.

" Maier-.1944. serial No. 537,665

aATENT, .OFFICE of March 3, 1883, as 28;]370 o. G. 757) chambers 36 and 38, in the normal condition, are

resiliently held to their maximum volume but may be contracted by negative pressure in the compartments 29 or 3|, chambers 36 or 38 may bereferred to as contraction chambers. Buier springs 60 and 62 arrest further downward movement of thediaphragms when the positive .pressure in chambers 36 or 38 becomes too great.

pulsating pump l64 comprises a pump cylinder v66 having a reciprocatory piston 68 slidable therein, anda connecting nod 'l0 hinged to a pump handle 'l2 at 14, the .pump handle being hinged at '|6` to a .bracket 18 extending from the cylinder`66. l The rotatable valve mechanism 80 has a valve body 82 which may -be cast integral with the cylinder I2 or made separately las desired. A cylindrical valve plug 84 is snugly fitted to the body82' but may be rotated through one quarter f turn'b'y means of the lever 86 which may be r"operated from a remote position by any suitable means' such as the rod 88.

The yinside of the valve lplug 84 is chambered outas at 90, and fluid from the pump `64 is ycarried through a main supplyv pipe 92 which connects with this chamber from the rear ithrough an opening 94 which is concentric with the plug. Diametrically opposite valve openings 96 "andu98 and another valve opening |00 spaced ninety A'degrees from the other two, extend from ther perimeter of the plug 84 radially inward into the chamber 90.

Spring loaded check valves |02 and |04 are biased' to prevent fluid iiow outward through the openings 96 and 98, respectively, and another The`V spaeeslaf anu so within @ne ses ujadits aregfhoweverj"connectedfto the*` tmospher ,by `50 anysitableopeningsias'at 52 :a d "S 56.1and`58aurge thefdiaphragms -lf'and K l n ward, whereas:the` negative .pressure i caused4 y y n movgmmbfi thempiston `I4 :to enlarge 'the com `@urges :them upward Since 65 "spring loaded valve |06 is biased to'prevent iluid flow inward through the opening |00. Fluid passagesl 01 and |08 lare provided for connecting the chambers 36 :and 38 to the several valve kopenings 9-6, 98, or |00. Since the setting of the *valve'mechanism 80 determines 'the direction which the servo piston |4 will'move, the valve mechanism 80 may preferably be called the selector` valve, and since the check valve |06 allows uid flow into the servomotor, it may be called theinflow check valve, while the check valves |02 and |04, being biased for flow out of the servomotor, may be termed outow check valves.

The system should be completely filled with hydraulic fluid Vwith the pump piston 68 and the y diaphragms 40 and 42 in the respective positions shownin Fig. 1 of the drawing. The operations.

of the device of Fig. 1 may preferably be carried out substantially as follows:

Let it be assumed, Vfor example, that it is desired to move the servo piston |4 to the right. The operator first positions the lever 86 of the selector valve as shown in Fig. 1 of the drawing. If the pump piston 68 is now moved left, fluid will 'be drawn from the contraction chamber 38, through the outflow check valve |04 to the pump. The large piston I4, however, can not at this time move right to replace the fluid drawn from the contraction chamber 38 because, while the pump 64 is drawing iiuid from the contraction chamber 38, it is also drawing the inflow check valve |06 shut, whereby no fluid may enter the contraction chamber 3-6, and therefore, since .the servo piston I4 may not move right, the diaphragm 42 rises to an upper position |09 by compressing the spring 58.

When, however, the direction of the pump piston 68 is reversed, i. e., moved to the right to the position shown, fiuid will be forced from the pump through the inflow check valve |06 into the contraction chamber 36 and through the opening 32 into the compartment 29 of the cylinder |2, whereupon the servo piston I4 moves right and the diaphragm 42 is brought back by the spring 58 from its upper position |09 to the normal position shown.

This completes one pump cycle. The distance which the servo piston I4 moves right per pump cycle depends, of course, on the relative displacements of the pump piston 68 and the servomotor piston I4.

Movement of the lever 86 of the selector valve clockwise through one quarter turn conditions the device of Fig. I for movement of the servo piston I4 to the left, since it provides the contraction chamber 36 with chamber-to-pump valving, and the contraction chamber 38 with pumpto-chamber valving which is the opposite of that shown in Fig. 1 of the drawing, whereby each pump cycle moves the servo piston I4 to the left an amount equal to that which it before moved to the right, in which case the chamber 36 instead of the chamber 38 will be contracted;

In the modification shown in Fig. 2, the servomotor has a cylinder ||2 with an elongated hollow piston ||4 slidable axially therein, and a piston rod ||6 extending axially from the piston. A disc I I8 is secured in the interior of the piston about midway of its length. Stops |20 and |22 are provided to limit axial movement of the piston in the cylinder. The piston rod ||6 has a 1ongitudinal opening |24 extending therethrough and the end is appropriately formed as at |26 for connection to the device which is to be operated.

Heads |28 and |30 close the ends of the cylinder I2, the hollow piston rod I I6 having sliding bearing in the head |30. The piston ||4 divides the space enclosed within the cylinder ||2 into two main compartments |28 and |3I. Passageways |32 and |34 extend through end enclosing portions |33 and |35 of the hollow piston ||4 to connect the chambers |36 and |38 with the main compartments |29 and |3|, the inner end walls of the compartments |29 and |3| being formed by the short pistons |40 and |42, respectively, which are slidably fitted to the interior of the elongated hollow piston ||4. The spaces |48 and |50 between the pistons |40 and |42 are connected together by the openings |44, and to the atmosphere by a series of connected passageways |46, |52, |24, and the transverse opening |54.

Springs |56 and |58 urge the pistons |40 and |42 toward each other, whereas the negative pressure caused by movement of the piston ||4 away from the heads |28 or |30 to thereby decrease the volume of the compartments |29 or |3| urges them to move farther apart. Since the chambers 36 and |38 are contracted by the presence of subatmospheric pressure in the compartments |29 or |3I, the chambers |36 and |38 may preferably be referred to as contraction chambers. Buffer springs |60 and |62 retard further movement of the pistons |40 and |42 toward each other when the positive pressure in contraction chambers |36 or |38 becomes too great.

A pulsating pump 64 which is an exact duplicate of that shown in Fig. 1 is employed in the modification shown in Fig. 2.

The rotatable valve mechanism has a valve body |82 which may be an integral part of the cylinder I I2 as seen in Fig. 1 or may be separated as shown. The rotatable valve |80 except for the difference in the body |82 is a duplicate of the rotatable valve 80 of Fig. l. Fluid conduits 201 and 208 are provided for connecting the contraction chambers |36 and |38 to the several valve openings 96, 98', or |00. Since the setting of the valve mechanism |80 determines the direction which the servo piston ||4 will move, the valve mechanism |80 may preferably be called the selector valve, and since the check valve |06 allows fluid flow into the servomotor, it may be called the inflow check valve, while the check valves |02 and |04, being biased for flow out of the servomotor, may be termed outiiow check valves.

The system should be completely filled with hydraulic fluid with the pump piston 68 and the narrow pistons |40 and |42 in the respective positions shown in the drawing.

The operation of the embodiment of Fig. 2 may preferably be carried out substantially as follows:

Let it be assumed, for example, that it is desired to move the servo piston ||4 to the right. The operator will first place the lever 86 of the selector valve in the position shown in the drawing. If the pump piston 68 is now moved left, fluid will be drawn from the compartment |3| and consequently from the contraction chamber |38 through the outflow check valve |04 to the pump. The elongated servo piston ||4, however, can not at this time move right to replace the fluid drawn from the contraction chamber |38 for the reason that, while the pump 64 is drawing fluid from the contraction chamber |38, it is also drawing the check valve |06 shut, whereby no fluid may enter the contraction chamber |36, and therefore, since the servo piston ||4 may not move right, the narrow piston |42 moves right by compressing the springs |58.

When, however, movement of the pump piston 68 is reversed so as to move to the right, to the position shown, fluid will be forced from the pump through the inflow check valve |06 into the compartment |29 and contraction chamber |36, whereupon the servo piston |4 moves to the right, and the narrow piston |42 is moved back, by the springs |58 to its normal position shown in the drawing.

This completes one pump cycle, the movement of servo piston ||4 per one pump cycle depending on the relative displacements of the pump piston and the servo piston.

Movement of the lever 86 of the selector valve clockwise through one quarter turn conditions the device of Fig. 2 for movement of the servo piston ||4 to the left, since it provides the contraction chamber |36 with chamber-to-pump valving and the chamber |38 with pump-tochamber valvingwhich is opposite to that shown in Fig. 2 of the drawing, whereby each pump cycle moves the servo piston ||4 to the left an amount equal to that which it before moved to the right.

From the foregoing description, it will be evident that the gist of the invention lies in providing pumping means capable of producing, in the main supply pipe, a flow of iluid alternating outward from the pump to the servomotor then back from the servomotor to the pump, with valv-v ing means which will direct the outward ow into one end of the iservo cylinder and withdraw fluid for backward flow from the other end of the servo Cylinder.

In the devices shown in Figs. 1 and 2 alternate flow in the main supply pipe is achieved by mere- 1y employing, as a pumping means, a piston, and a cylinder with one end closed, whereby movement of the piston toward the closed end causes outward ilow of iiuid in the supply pipe, and movement of the piston away from the closed end causes return flow of uid in the supply pipe.

There are, however, situations where a pump of uniform delivery such as a sliding vane pump or a gear pump is preferably employed. In such a situation, means is necessarily provided for causing the uniform `flow from the discharge side of the uniform delivery pump to flow rst in one direction then in the other within the supplyA pipe. Such an arrangement is shown in Fig. 3 of the drawing.

Referring now to Fig. 3, a power driven gear pump 2|8 has its suction lside 2|2 connected by a pipe 2|4 to a supply tank 2|6 and its discharge side 2|8 connected by a pipe 220 to the inlet side 222 of an automatic valve 224, the outlet side 226 of the valve 224 being connected by a pipe 228 to the main supply line 238, the function of the automatic valve 224 being to create an alternating fluid flow in the supply pipe 238.

The automatic valve 224 has a body 232 with a cylindrical bore 234 adapted to slidably receive a. small piston 236. Piston 236 .is resiliently held against the bottom wall of the cylindrical bore 234 by a spring 238. A piston rod 248 extends downwardly from the piston through the bottom wall of the bore 234 into a compression chamber 242. Piston rod 248 has a laterally extending bracket 244, the outer end of which supports the valve heads 246 and 248 which are on a common stem which is vertically slidable in the bracket.

Springs 258 around the stem above and below the bracket cushion the seating of the valve heads. When the upper head 246 is oi its seat, the pressure chamber 242 is in communication with the valve outlet 226, and when the valve head 248 is oil its seat, the pressure chamber 242 is in communication, through a short pipe 252, with the return pipe 254 which leads back to the pump inlet 2|2.

The piston 236 has a groove 256 around it, which, when the piston moves upward, connects the valve outlet 226 to the return pipe 254. A small spring loaded ball valve 258 allows such fluid as leaks past the upper end of the Piston to return through the pipe 268 to the return pipe 254.

An emergency hand pump 262 i's provided in case the power pump 2 I 8 should fail. Hand pump 262 has a cylinder 264 with piston 266 operated through a connecting rod 268 by handle 218. Hand pump 262 draws fluid by way of the pipe 212 from the same source as the power pump.

Conventional valves 214 and 216 are placed in the bottom of the cylinder and in the piston respectively. A discharge pipe 218 delivers the fluid from the hand pump to a pressure tank 288. 'A valve 282 may be turned by the handle 284 to connect the pressure tank 288 through the inlet 222 to the compression chamber 242.

The hydraulic servomotor 3|8, which is operated by means of the alternating flow in the supply pipe 238, comprises a cylinder 3|2 in which a pistn 3|4 is axially slidable. Piston 3|4 is mounted on a piston rod 3| 6, the piston being secured against axial movement on the rod by nuts 3|8. Stops 328 and 322 are provided to limit the axial movement of the .piston in the cylinder. -The end 326 of the piston rod is suitably formed for connection to the device which is to be operated.

The ends of the cylinder 3|2 are closed by heads 328 and 338, the head 338 providing bearing for the piston rod 3|6. 'Ihe piston 3| 4 divides the enclosed space within the cylinder 3|2 into compartments 329 and 33|. Passageways 332 and 334 extend through the cylinder walls from the compartments 329 and 33| into chambers 336 and 338, respectively, these chambers being closed on the underside by the flexible diaphragms 348 and 342, respectively. Caps 344 and 346 clamp the diaphragms in place, thus making the chambers 336 and 338 pressure tight. The spaces 348 and 358 within the caps 344 and 346 are, however, connected to the atmosphere .by any suitable openings as at 352 and 354. Springs 356 and 358 normally hold the diaphragms in the upwardly deected position shown while a positive pressure of a predetermined value in the chambers 336 or 338 forces the diaphragms to an equally deflected downward position 34| and 343. Since the chambers 336' and 338 are adapted to expand from their normal volume by superatmospheric pressure in the compartments 329 and 33|, the chambers 336 and 338 may be referred to as expansion chambers. l

The rotatable selector valve mechanism 388 has a valve body 382 which may be cast integral with the cylinder 3|2 or made separately if so desired. A cylindrical valve plug 384 is snugly fitted to the body 382 but may be rotated through one quarter turn Vby means of the lever 386 which may be remotely controlled as by a cable 388 'and returned to normal position by a spring 389. A lever 39| within convenient reach of the oper ator is provided for drawing up the cable.

The inside of the valve plug 384 is chambered out as at 398, uid from the automatic valve 224 alternately owing to and from the chamber 398 by way of the, long supply pipe 238 which connects to this chamber from the rear through an opening 394 which is concentric with the plug. Diametrically opposite valve openings 396 and 388, and another valve opening 488 spaced ninety degrees from the other two, extend from the perimeter of the plug 384 radially inward into the chamber 398.

Spring loaded outflow check valves 482 and 484 are biased to allow uid flow outward through the openings 396 and 398, respectively, and another spring loaded inflow check valve 486 is biased to allow now inward through the opening 488. Fluid passages 481 and 488 are provided for connecting the chambers 336 and 338 to the several valve openings 396, 398, and 488. The system should be completely illled with the hydraulic fluid when the diaphragms 348 and 342 are in the positions shown in Fig. 3 of the drawing. Fluid will then be added from the tank 2 I6 if and when it is required. The operation of the device of Fig. 3 may preferably be carried out substantially as follows:

Let it be assumed, for example, that it is desired to move the servo piston 3 4 to the right. The operator will first place the lever 386 of the selector valve as shown in Fig. 3 of the drawing. If the power pump 2|0 is now operating, fluid will flow from the pump outlet 2| 8 into the automatic valve at 222, into the compression chamber 242 and out past the valve head 246 which is now unseated, through 226, 228 and the main supply pipe 230 in which the uid moves to the right, entering the selector valve chamber 390 and flowing thence through the inow check valve 406 into the expansion chamber 336.

Continuing flow into expansion chamber 336 deflects the diaphragm 340 downward to the position 34|, then moves the piston 3 I4 to the right far enough to force the diaphragm 342 down to the position 343; then the piston 3| 4 must stop because there is no outflow through the passage 408 because the pressure in the chamber 390 is holding the outflow check valve 404 closed.

When the servo piston 3|4 stops moving to the right, the pressure builds up in the compression chamber 242 of the automatic valve, causing the piston rod 240 to rise, thus seating the valve head 246, unseating the valve head 248, and connecting the opening 226 to the return pipe 254 by means of the piston groove 256.

When the lower valve head 248 is unseated, the pump 2|0 wil1 merely circulate fluid through the short pipe 252 back to the return pipe 254, and while it is so circulating the fluid, the diaphragm springs 356 and 358 move the diaphragms 340 and 342 back from their deflected positions 34| and 343 to their normal positions 340 and 342.

It is noted that, since the bottom of the piston rod 240 is -only slightly larger than the top of the valve head 248, the pressure will be quite high in the servo motor 3|0 and in the chamber 242 before the piston rod 240 will rise, for the reason that the force tendingto raise the piston rod is only the difference between the upward force on the piston rod and the downward force on the valve head.

After the piston 236 has moved to its upper position, a slight pressure will still build up in the chamber 242 due to the resistance to flow in the piping, and this pressure may be accurately controlled by the size of the opening through the pipe 252, and should be such as would exert an upward force on the piston rod 240 which is slightly less than the downward force of the light spring 238, for otherwise the piston 236 would continue indefinitely in the upper position.

As long, however, as the heavy springs 356 and 358 are returning uid under heavy pressure to upward, the fluid displaced in expansion chamber 336 can not get out of valve 406 so it moves the servo piston 3 4 again to the right. The fluid displaced by movement of the servo piston 3|4 to the right plus the fluid displaced by the upward movement of the diaphragm 342 all passes out through passage `408 and outflow check valve 404 into the supply pipe 230 where it moves to the left. then out through pipe 228, opening 226, piston groove 256 to return pipe 254.

While the servomotor was returning fluid back to the pump intake 2|2 by way of the piston groove 256, and the pump was circulating fluid from its discharge side back to its suction side by way of the unseated valve head 248 and pipe 252, the pressure dropped in the chamber 242, thereby allowing the spring 238 to reseat the valve head 248, unseat the valve head 246, and return the piston groove 256 to normal, all as shown in Fig. 3 of the drawing, at which point the mechanism starts all over to repeat the cycle.

From the foregoing description it may be seen that, with the valve plug 364 set as shown, the servo piston 3|4 is moved to the right by flow of fluid in the pipe 230 whether the flow is to the right or to the left in the pipe, whereby the movement of the piston is substantially constant.

In the drawing, Fig. 3, the selector valve 380 is set for moving the servo piston to the right. Movement of the selector valve lever 386 through one quarter turn by the control lever 39| will set the valve for movement of the servo piston to the left. v

Other modications, variants and equivalents are intended to be embraced in the following claims.

I claim:

1. A hydraulic system comprising, in combination, a servomotor having two fluid compartments, fluid actuated means movable by increase of the fluid volume in one compartment and deand through the opening 226, the piston 236 will i remain in the upper position for the reason that, as soon as the piston yields to the light spring 238 and starts to move down, the valve 246 is slightly opened, whereby the slight pressure in the chamber 242 caused by the resistance in the piping is supplemented by the higher pressure of the servomotor entering the chamber 242 through the valve 246. The piston 236 may therefore return to its lower position only when the springs 356 and 356 have put the diaphragm 340 and 342 back to their normal position, i. e., when the uid which rst moved rightwise through the pipe 230 to the servomotor 3 0 has now returned leftwise through the same pipe 230.

When the diaphragms 340 and 342 thus move crease of the uid volume in the other compartment, power take-oir means associated with said fluid actuated means, a chamber in direct communication with each compartment, said chambers each including a dsplaceable means for varying their volumetric capacity when the amount of fluid is altered therein without a corresponding movement of the fluid actuated means, a single long fluid transfer pipe having one end proximate said compartments and the other end remote therefrom, a fluid transfer means for moving fluid into one of said compartments and withdrawing fluid from the other of said compartments, said fluid transfer means including first, a pump connected to the remote end of said long transfer pipe, second, resilient means for restoring said displaceable means after said displaceable means have been displaced for varying the volumetric capacity of said chambers, and third, a valve mechanism for alternately connecting said proximate end to one compartment when the ilow is in one direction and to the other compartment when the flow is in the other direction, and selector means shiftable to reverse the connections of said valve mechanism, whereby, before the shift, said proximate end may be connected to a given compartment for one direction of flow and, after the shift, be connected to the same compartment but for the other direction of flow.

2. In a hydraulic system as defined in claim 1, wherein the fluid moving means comprises a uniform delivery pump and an automatic valve for converting said uniform delivery into an alternatchamber, an arm extending laterally from said rod, a valve stem carried at the end of said arm .and slidable axially in an opening in said arm, a

' tween said short pistons, dividing the space bevalve head on each end of said stem, valve seats y in opposite walls of said compremion chamber spaced apart so that movement of said piston in one direction seats one valve head and movement of the piston in the other direction seats the other valve head, conduit means connecting the one valve seat to said pipe, conduit means connecting the other valve seat to the suction side of said uniform delivery pump, conduit means connecting the compression chamber to the discharge side of said uniform delivery pump, and a port valve in said piston, operative upon movement'of said pistonby pressure in said compression chamber to connect said long pipe to the suction side of said uniform delivery pump.

3. A hydraulic system comprising, in combination, a closed main cylinder, a piston in said main cylinder dividing the space within said main cylinder into two compartments, a piston rod fast in said piston and slidable in the ends of said main cylinder, an expansion chamber alongside each compartment in direct communication therewith,

said expansion chambers each including a diaphragm as one wall thereof and spring means urging said diaphragm outwardly, the diaphragms being deilectible inwardly against the force of the spriir'ig means when the volumetric capacity of a chamber is reduced by withdrawing fluid from the chamber without corresponding movement of said piston, valve mechanism operable to two positions for controlling ilow into and out of said chambers, said valve mechanism having a common uid passageway for ilow within the body of. said valve mechanism and a series of check valves communicating with said common fluid passageway and biased, in one position, for inow into one chamber and outflow from the other, and biased, in another position, for outflow from the said one chamber and inilow into the said other, a pump cylinder having a piston slidable therein remotely located from the main cylinder. and a long pipe connecting the outlet opening of the pump cylinder to said common duid passageway of the valve mechanism.

4. A hydraulic system comprising, in combination, a closed cylinder, a relatively long internally bored main piston slidable in said cylinder dividing the space within said cylinder into two compartments, a piston rod extending from said piston and slidable through an opening in the end oi' said cylinder, two relatively short spaced apart pistons slidable axially in the bote ol the main tween said short pistons into two smaller spaces, butler springs in said smaller spaces urging said short pistons away from said partitioning memberl expansion spring means between said short pistons and the ends of the main piston urging said short pistons toward each other, the ends of said main piston having end enclosing portions which partly close the ends of the main piston and denne contraction chambers between the short pistons and said end enclosing portions, leaving passageways connecting the compartments to the contraction chambers, said end enclosing portions serving as supporting means for the outer ends of said expansion springs, conduit means extending through said partitioning member and through the wall of said main piston and piston rod, to the atmosphere, valve mechanism operable to two positions for controlling flow into and out of said compartments and said contraction chambers, said valve mechanism having a common fluid passageway for flow within the body ol' said valve mechanism and a series of check valves communicating with said common uid passageway Vand biased, in one position, for inflow into one compartment and contraction chamber and outflow from the other compartment and contraction chamber, and biased, in another position, for outflow from the said one compartment and contraction chamber and inow into the said other compartment and contraction chamber, piping connecting the passageway through said check valves to the two compartments, a pump cylinder having a piston slidable therein remotely located from the main cylinder, and a long vpipe connecting the outlet opening of the pump cylinder to the said common fluid passageway of the valve mechanism.

y NASSER D. OWEN.

REFERENCES crrEn The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 16,801 lindsay Mar. 10, 1857 1,177,385 Conradson -.f Mar. 28, 1916 1,185,333 Keltner May 30, 1916 1,195,141 Kenney Aug. 15, 1916 1,343,117 Dana Jan. 8, 1920 1,409,441 Harper Mar. 14. 1922 1,806,136 Weiss May 19, 1931 2,200,392 Goldberg May 14, 1940 2,241,056 Chilton May 8, 1941 2,359,949 van Der Werl! Oct 10, 1944 

